Munitions, such as missiles and rockets, are often launched from canisters. The canisters are typically round or square tubes that contain a munition, munition-launch hardware such as rails and/or sabots, and electronics for initiating launch. In addition to functioning as a launch system, the canisters provide environmental protection for the munition, simplify munition-handling issues, and provide an efficient and long-term munition-storage solution.
In order to provide full environmental protection for the munition and other components within the canister, the canister must be sealed. This is typically done using a cap or cover. The cover is ideally able to protect or isolate the munition from a variety of environmental factors, such as variations in humidity, temperature extremes, debris impact from transportation or from the launch of adjacent munitions, exposure to water, icing, electromagnetic interference, etc. Furthermore, the cover is preferably resistant to degradation from the nuclear, biological and chemical decontaminants, corrosion, flame, and pressure. Also, it is desirable for the cover to provide some degree of acoustical dampening. And, importantly, the canister cover must provide unimpeded passage of the munition upon launch.
Several types of canister covers are known. One type comprises a flexible membrane that is stretched over a frame that is permanently attached to the canister. Upon launch, the munition tears through the membrane. Disadvantages of this type of cover are that it has relatively limited durability, offers minimal environmental protection, and is an inefficient storage solution due to the space required for the frame that attaches the membrane to the canister.
A second type of canister cover is a hard cover, typically made of plastic or metal, which is bonded to the canister. Upon launch, the cover is blown off the canister due to launch pressure or the forward motion of the munition. In some versions of this cover, the cover is scored to enable it to break into a predetermined number of pieces having a desired size. Drawbacks of this cover include a requirement that the launch pressure be relatively high to break the cover or the bond between the cover and the canister, inconsistent breaking of the bond between the cover and the canister, damage to the munition caused by impact with the cover, and damage to launch equipment due to cover fragments.
A third type of canister cover is a foamed plastic cover, which incorporates a solid layer of plastic foam. Upon launch, the canistered munition strikes the cover, which then breaks into pieces. These covers disadvantageously provide a poor environmental seal because the foam is a porous material that has limited resistance to air or moisture. Furthermore, because foamed plastic is hard and brittle, it is difficult to attach it to a canister without breaking or cracking the foam.
A fourth type of canister cover is a glass cover. The glass is heat treated so that it becomes frangible (i.e., a small point load will completely shatter it). The size of the shattered pieces can be predetermined and controlled by varying the heat treatment. But a cover formed of tempered glass has low overall durability due to the ease with which the glass can shatter. For example, such a cover will typically fail when exposed to hail. Furthermore, the glass fragments can interfere with launch of the munition by becoming wedged between the munition and the inner surface of the canister. Additionally, glass fragments can also scratch the surface of the munition, which might affect its aerodynamics.
Although known canister covers provide a varying measure of protection against at least some of environmental conditions, none of them are able to satisfy all of the internal and external environmental requirements pertaining to:                extremes of temperature;        nuclear, biological, and chemical (“NBC”) decontaminants;        hail impact;        electromagnetic interference (“EMI”);        low vapor permeability;        corrosion resistance and flammability;        acoustical dampening;        internal and external pressure containment; and        limitations on the outgassing of internal materials (e.g., TML<1.0%, CVCM<0.10%) IAW ASTM E595.        